The present invention relates to diene rubber compositions reinforced with white fillers, which can be used for the manufacture of tires or semi-finished products for tires and, in particular, tire treads.
The invention pertains to an aluminum based reinforcing white filler and to diene rubber compositions containing this filler.
In order to reduce fuel consumption and pollution emitted by motor vehicles, major attempts have been made by tire designers to obtain tires having all of the following characterisics: very low rolling resistance, improved grip both on dry ground and on wet or snow-covered ground, and very good wear resistance.
Numerous solutions have thus been proposed to lower the rolling resistance and to improve the grip of tires, but these have generally resulted in a very great decline in the wear resistance.
It is well known that the incorporation of conventional white fillers, such as silica (SiO2), alumina (Al2O3), titanium oxide (TiO2), chalk, talc, clays such as bentonite or kaolin for example, in rubber compositions used for the manufacture of tires and, in particular, of treads, results in a reduction in the rolling resistance and an improvement in grip to wet, snow-covered or icy ground. However, it also results in an unacceptable decline in the wear resistance because these conventional white fillers do not have sufficient reinforcement ability with respect to such rubber compositions. For this reason, these white fillers are generally referred to as non-reinforcing fillers, or alternatively inert fillers.
One effective solution to this problem was described in Patent Application EP-A-0 501 227, which discloses a sulphur-vulcanizable diene rubber composition obtained by thermo-mechanical working of a conjugated diene copolymer and an aromatic vinyl compound prepared by solution polymerization. This composition also comprises a special highly dispersible precipitated silica as reinforcing white filler. This composition makes it possible to manufacture a tire having substantially improved rolling resistance, without affecting the other properties, in particular those of grip, endurance and, above all, wear resistance.
Other compositions having such an excellent balance between several contradictory properties would be of great interest to tire manufacturers, who would thus have different choices available to them. Furthermore, the improvement in wear resistance thus obtained might possibly be converted into a lowering of the rolling resistance by reducing the thickness of the tread. It would thus be conceivable to construct tires having an unchanged life, but which are lighter and therefore consume less energy.
During the course of their research, the Inventors have discovered a novel reinforcing white aluminum-based filler, based on an aluminum compound, which unexpectedly makes it possible to obtain a level of reinforcement at least equal to that obtained with highly dispersible silicas.
The invention relates to a reinforcing aluminum-based filler which can be used for reinforcing diene rubber compositions intended for the manufacture of tires. The filler comprises an aluminum (oxide-)hydroxide corresponding, with the exception of any impurities and the water of hydration, to the general Formula I (a and b being real numbers):
Al (OH)aOb, where: 0 less than axe2x89xa63 and b =(3-a)/2,xe2x80x83xe2x80x83(I)
the specific BET surface area of which is between 30 and 400 m2/g, the average particle size (by mass) dw of which is between 20 and 400 nm and the disagglomeration rate, xcex1, of which, measured via the ultrasound disagglomeration test, at 100% power of a 600-watt ultrasonic probe, is greater than 5xc3x9710xe2x88x923 xcexcm-xe2x88x921/s.
Aluminum oxides or hydroxides have already been described as various additives in rubber compositions for tires. By way of example, Patent Application EP-A-0 697 432 describes the use of various inorganic powders of Al, Mg, Ti, Ca, or of oxides or hydroxides of these elements, in particular alumina (Al2O3) or aluminum tri-hydroxide Al (OH)3, with the aim of improving braking and grip performance on wet ground. However, these inert fillers have neither the function nor the abilities of reinforcing fillers in the rubber compositions described. The compositions are reinforced in conventional manner by carbon black, with which silica and a coupling agent for this silica may possibly be associated.
Thus, to the Inventors"" knowledge, the prior art neither describes nor suggests the present aluminum-based filler which, because of its characteristics, is capable on its own of reinforcing diene rubber compositions useful in the manufacture of tires. Such compositions have substantially the advantageous properties of the silica-based compositions described in the above-mentioned Patent Application EP-A-0 501 227.
A second subject of the invention relates to a process for obtaining an aluminum-based filler according to the invention, comprising:
(i) reacting an aqueous solution of a Bronsted base under stirring with an aqueous solution of an aluminum salt in order to precipitate the aluminum salt in a suspension of aluminum hydroxide;
(ii) filtering the suspension thus obtained and washing it with water;
(iii) drying the filtrate thus obtained with a drying means suitable for limiting the agglomeration of the particles of hydroxide upon elimination of the water; and
(iv) then heat-treating the compound thus obtained so as to obtain an aluminum (oxide-)hydroxide.
Another subject of the invention relates to a sulphur-vulcanizable rubber composition which can be used for the manufacture of tires, comprising at least one diene elastomer, a reinforcing white filler and a coupling agent linking the reinforcing filler and the elastomer, wherein the white filler is formed in its entirety or in part by an aluminum-based filler according to the invention.
Another subject of the invention is a process for reinforcing a diene rubber composition which can be used for the manufacture of tires, comprising incorporating an aluminum-based filler according to the invention into the composition by mixing in an internal mixer, before introducing the vulcanization system.
Another subject of the invention is the use, as reinforcing filler, of an aluminum-based filler according to the invention in a diene rubber composition which can be used for manufacturing tires.
Another subject of the invention is the use of a rubber composition according to the invention for the manufacture of rubber articles, in particular tires or semi-finished products intended for such tires, these semi-finished articles being selected from the group consisting of treads, underlayers intended, for example, to be positioned beneath these treads, crown plies, sidewalls, carcass plies, beads, protectors, inner tubes and airtight internal rubbers for tubeless tires. The invention relates more particularly to the use of such a rubber composition for the manufacture of the sidewalls or treads, owing to its good hysteretic properties.
The composition according to the invention is particularly suitable for the construction of treads for tires intended to be fitted on passenger vehicles, vans, two-wheelers and heavy vehicles, aircraft, construction, agricultural or handling machinery, wherein such treads are usable in the manufacture of new tires or for recapping worn tires.
The subject of the invention is also such tires and rubber articles themselves when they comprise a rubber composition according to the invention.